Colostomy is a surgical procedure to connect a patient's colon to an artificial anus, usually called a stoma, formed in the abdominal wall. Having undergone a colostomy the patient must always keep a colostomy bag in position against the stoma to receive feces and gas discharged through the stoma. An abdominal belt is usually used to hold the bag in position against the stoma immediately behind the normal beltline of a patient's clothing, where the clothing is normally tightest. In addition, the bag is normally provided with a gas vent to prevent gas build up and over inflation of the bag, and in order to eliminate offensive odours caused by the escaping gas it is common practice to provide an exterior deodorizing filter in the gas vent line. Attention is directed to U.S. Pat. No. 6,007,525 issued 18 Dec. 1999 and U.S. Pat. No. 7,090,664 issued 15 Aug. 2006 as illustrative of present colostomy bags. While these bags are generally effective to release the gases in a discreet and odourless manner, there remains the problem that the gas vent tube is placed near the top of the bag and adjacent to the stoma. Feces entering the bag from the stoma are frequently squeezed sideways and upwardly by the pressure of the patient's belt or waistband rather than falling under gravity to the bottom of the bag, with the result that the relatively narrow vent tube becomes plugged and the bag has to be removed prematurely for cleaning. In U.S. Pat. No. 7,090,664 an attempt to overcome this problem has been suggested by the provision of a short horizontal baffle to protect the vent tube from ingress of feces, but this is not entirely satisfactory and does not eliminate the problem.